Ultra-Wideband (UWB) technology is a wireless technology for the transmission of digital data as modulated coded impulses over a very wide frequency spectrum with very low power over a short distance. Such pulse based transmissions are an alternative to transmitting information using a modulated sinusoidal wave, which is the technique currently employed within today's wireless communication standards and systems such as IEEE 802.11 (Wi-Fi), IEEE 802.15 wireless personal area networks (PANs), IEEE 802.16 (WiMAX), Universal Mobile Telecommunications System (UMTS), Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), and those accessing the Industrial, Scientific and Medical (ISM) bands, and International Mobile Telecommunications-2000 (IMT-2000).
UWB was formerly known as “pulse radio”, but the Federal Communications Commission (FCC) and the International Telecommunication Union Radiocommunication Sector (ITU-R) currently define UWB in terms of a transmission from an antenna for which the emitted signal bandwidth exceeds the lesser of 500 MHz or 20% of the center frequency. Thus, pulse-based systems where each transmitted pulse occupies the full UWB bandwidth or an aggregate of at least 500 MHz of narrow-band carriers; for example, orthogonal frequency-division multiplexing (OFDM) can gain access to the UWB spectrum under the rules. Pulse repetition rates may be either low or very high. Pulse-based UWB radars and imaging systems tend to use low to moderate repetition rates (typically in the range of 1 to 100 megapulses per second). On the other hand, communications systems favor high repetition rates (typically in the range of one to two gigapulses per second), thus enabling short-range gigabit-per-second communications systems. As each pulse in a pulse-based UWB system occupies a large bandwidth, possibly even the entire UWB bandwidth, such systems are relatively immune to multipath fading but not intersymbol interference, unlike carrier modulation based systems which are subject to both deep fading and intersymbol interference (ISI).
Pulse based wireless communication has come a long way since being first allowed by the Federal Communication Commission (FCC). Able to offer both high data rates and very energy efficient transmissions over short ranges, multiple techniques have been developed for ultra-wideband (UWB) communication including multi-band orthogonal frequency division multiplexing (MB-OFDM), impulse radio (IR-UWB) and frequency modulation (FM-UWB) each with its specific strengths. The potential for very low power communications and precise ranging has seen the inclusion of UWB radios in multiple standards aimed for different applications such as low-rate wireless personal area networks (WPAN) with IEEE 802.15.4a and more recently wireless body area networks (WBAN) with IEEE 802.15.6.
When considering many applications, such as wireless sensor networks and portable electronics, UWB transceivers should ideally be functionally highly integrated for small footprint, support low cost and high volume manufacturing, and be energy efficient in order to run on a limited power source, e.g. a battery, indoor solar cell, small outdoor solar cell, or those developed upon evolving technologies such as thermal gradients, fluid flow, small fuel cells, piezoelectric energy harvesters, micro-machined batteries, and power over optical fiber. UWB has been considered for a long time a promising technology for these applications. By using discrete pulses as modulation, it is possible to implement efficient duty cycling schemes while the transmitter is not active, which can be further improved by using an On-Off Shift Keying (OOK) modulation. Further, some UWB operation frequencies, between 3.1 GHz and 10.6 GHz for example as approved by FCC for indoor UWB communication systems, see for example “First Report and Order in the Matter of Revision of Part 15 of the Commission's Rules Regarding Ultra-Wideband Transmission Systems” (FCC, ET-Docket 98-153, FCC 02-48), allow for small antennas which can easily be integrated into overall reduced footprint solutions such as sensors, mobile devices or portable electronics etc.
To date the primary applications for UWB networks have been high data rate personal area and local area networks (PANs/LANs) to exploit the increased data rates achievable over distances on the order of 50 meters. As such UWB (IEEE 802.15.3) sits within a set of wireless protocols including IEEE 802.15.1 (Bluetooth), IEEE 802.15.4 (ZigBee) and IEEE 802.11a/b/g (Wi-Fi) defining physical (PHY) and media access control (MAC) layers of wireless communications over ranges around 10-100 meters. In contrast to the other wireless protocols UWB offers lower complexity and cost, resistance to severe multipath interference and jamming (which is of particular benefit within indoor environments), a noise-like signal spectrum, and good time domain resolution for location and tracking applications.
Within the prior art the primary focus of the majority of wireless communications research has been concerned with maximizing utilization of narrow frequency spectrum, e.g. cellular wireless through GSM, EDGE, LTE, 4G etc., or maximizing link speeds, e.g. WiMAX (IEEE 802.16), Wi-Fi (IEEE 802.11n) etc. However, in a wide range of applications such as wearable devices, wireless location services, wireless sensor networks, etc. conventional wireless protocols as well as PAN/LAN protocols such as IEEE 802.15.1 (Bluetooth), IEEE 802.15.4 (Zigbee), and IEEE 802.11a/b/g (Wi-Fi) cannot meet the evolving requirements for ultra-efficient wireless communications and ultra-low power consumption particularly at the lower data rates many of these applications operate at due to their inherent architecture, communication layer or limited duty cycling ability.
Whilst efficiencies with IEEE 802.15.1 (Bluetooth) and IEEE 802.15.4 (Zigbee) on the order of approximately 50 nJ per bit are possible and innovative designs are attempting to further lower this figure, the narrowband signaling scheme used for communications in these systems and their reliance on traditional RF transceiver architectures severely limits the achievable energy efficiency, especially at lower data rates such as below 1 Mbps. Further, it is important that the peak power consumption not exceed that supportable by common battery technologies or energy harvesting technologies nor long term power consumption be too high such that battery lifetimes are very limited or alternate energy sources such as solar cells cannot sustain them.
Accordingly, it would be beneficial to rethink the entire transceiver structure and the communication scheme employed in order to achieve the sub nJ per bit energy efficiencies required by next generation applications.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.